U.S. patent number 8,911,881 [Application Number 11/256,954] was granted by the patent office on 2014-12-16 for organic light-emitting device.
This patent grant is currently assigned to Samsung Display Co., Ltd.. The grantee listed for this patent is Yong-Joong Choi, Min-Seung Chun, Jun-Yeob Lee. Invention is credited to Yong-Joong Choi, Min-Seung Chun, Jun-Yeob Lee.
United States Patent |
8,911,881 |
Lee , et al. |
December 16, 2014 |
Organic light-emitting device
Abstract
An organic light-emitting device is provided. The organic
light-emitting device comprises a first electrode, a second
electrode, and a light-emitting layer interposed between the first
electrode and the second electrode. The device further comprises of
a phosphorescent dopant and a phosphorescent host that includes at
least two hole transport materials. The mixed phosphorescent host
materials increase energy transfer efficiency, thereby improving
the efficiency and lifespan of the resulting organic light-emitting
device.
Inventors: |
Lee; Jun-Yeob (Suwon-si,
KR), Chun; Min-Seung (Suwon-si, KR), Choi;
Yong-Joong (Suwon-si, KR) |
Applicant: |
Name |
City |
State |
Country |
Type |
Lee; Jun-Yeob
Chun; Min-Seung
Choi; Yong-Joong |
Suwon-si
Suwon-si
Suwon-si |
N/A
N/A
N/A |
KR
KR
KR |
|
|
Assignee: |
Samsung Display Co., Ltd.
(Yongin, KR)
|
Family
ID: |
35768103 |
Appl.
No.: |
11/256,954 |
Filed: |
October 25, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060099447 A1 |
May 11, 2006 |
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Foreign Application Priority Data
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Nov 5, 2004 [KR] |
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10-2004-0089651 |
Nov 27, 2004 [KR] |
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10-2004-0098370 |
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Current U.S.
Class: |
428/690; 428/917;
313/504 |
Current CPC
Class: |
H01L
51/5016 (20130101); C09K 11/06 (20130101); H05B
33/14 (20130101); C09K 2211/181 (20130101); C09K
2211/1029 (20130101); H01L 51/0081 (20130101); C09K
2211/186 (20130101); C09K 2211/1044 (20130101); C09K
2211/1014 (20130101); H01L 51/0085 (20130101); Y10S
428/917 (20130101); H01L 51/0072 (20130101); H01L
51/0071 (20130101); H01L 51/006 (20130101) |
Current International
Class: |
H01L
51/54 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1474639 |
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Feb 2004 |
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CN |
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2002-313583 |
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Oct 2002 |
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JP |
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2003-007467 |
|
Jan 2003 |
|
JP |
|
2004-022544 |
|
Jan 2004 |
|
JP |
|
2004-296185 |
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Oct 2004 |
|
JP |
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1020030041972 |
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May 2003 |
|
KR |
|
10-2003-0097363 |
|
Dec 2003 |
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KR |
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1020030093242 |
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Dec 2003 |
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KR |
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WO 2005/029923 |
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Mar 2005 |
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WO |
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Other References
European Search Report dated Feb. 24, 2006. cited by applicant
.
Xiong Gong, et al., "Phosphorescence From Iridium Complexes Doped
Into Polymer Blends", Journal of Applied Physics, vol. 95, No. 3,
pp. 948-953, Feb. 1, 2004. cited by applicant .
Kathleen M. Vaeth, et al., "High-Efficiency Doped Polymeric Organic
Light-Emitting Diodes", Journal of Polymer Science, vol. 41, pp.
2715-2725, 2003. cited by applicant .
Noriyuki Matsusue, et al., "Charge Carrier Transport in an Emissive
Layer of Green Electrophosphorescent Devices", Applied Physics
Letters, vol. 85, No. 18, pp. 4046-4048, Nov. 1, 2004. cited by
applicant .
Chinese Office Action dated Dec. 26, 2008. cited by
applicant.
|
Primary Examiner: Yamnitzky; Marie R.
Attorney, Agent or Firm: H.C. Park & Associates, PLC
Claims
What is claimed is:
1. An organic light-emitting device, comprising: a first electrode;
a second electrode; and a light-emitting layer interposed between
the first electrode and the second electrode, wherein the
light-emitting layer consists of a phosphorescent dopant and two
phosphorescent hosts, wherein the two phosphorescent hosts are
4,4'-biscarbazolylbiphenyl (CBP) and
4,4'-biscarbazolyl-2,2'-dimethylbiphenyl (dmCBP), and wherein CBP
and dmCBP are combined in a weight ratio of about 1:3 to about
3:1.
2. The organic light-emitting device of claim 1, wherein the
light-emitting layer consists of about 70 parts by weight to about
99 parts by weight of the two phosphorescent hosts and about 1 part
by weight to about 30 parts by weight of the phosphorescent
dopant.
3. The organic light-emitting device of claim 1, further comprising
at least one of a hole injection layer and a hole transport layer
interposed between the first electrode and the light-emitting
layer.
4. The organic light-emitting device of claim 1, further comprising
at least one of a hole blocking layer, an electron transport layer,
and an electron injection layer interposed between the
light-emitting layer and the second electrode.
5. An organic light-emitting device, comprising: a first electrode;
a second electrode; and a light-emitting layer interposed between
the first electrode and the second electrode; wherein the
light-emitting layer consists of: a phosphorescent dopant; a first
phosphorescent host having a triplet energy of about 2.3 eV to
about 3.5 eV; and a second phosphorescent host having a triplet
energy of about 2.3 eV to about 3.5 eV, wherein the first
phosphorescent host and the second phosphorescent host have
different highest occupied molecular orbital (HOMO) energy levels
and/or different lowest unoccupied molecular orbital (LUMO) energy
levels, wherein the phosphorescent dopant is one material selected
from the group consisting of bis(thienylpyridine) acetylacetonate
iridium and bis(1-phenylisoquinoline)iridium acetylacetonate,
wherein the first phosphorescent host and the second phosphorescent
host are combined in a weight ratio of about 1:3 to about 3:1, and
wherein the first phosphorescent host is 4,4'-biscarbazolylbiphenyl
(CBP) and the second phosphorescent host is
4,4'-biscarbazolyl-2,2'-dimethylbiphenyl (dmCBP).
6. The organic light-emitting device of claim 5, wherein the
light-emitting layer consists of about 70 parts by weight to about
99 parts by weight of the phosphorescent hosts and about 1 part by
weight to about 30 parts by weight of the phosphorescent
dopant.
7. The organic light-emitting device of claim 5, further comprising
at least one of a hole injection layer and a hole transport layer
interposed between the first electrode and the light-emitting
layer.
8. The organic light-emitting device of claim 5, further comprising
at least one of a hole blocking layer, an electron transport layer,
and an electron injection layer interposed between the
light-emitting layer and the second electrode.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims priority to and the benefit of Korean
Patent Application No. 10-2004-0089651 filed on Nov. 5, 2004, in
the Korean Intellectual Property Office, and Korean Patent
Application No. 10-2004-0098370 filed on Nov. 27, 2004, in the
Korean Intellectual Property Office, the disclosures of which are
incorporated herein in their entirety by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an organic light-emitting device
in which at least two hole transport materials are used as
phosphorescent hosts, thereby improving the efficiency and the
lifespan of the device.
2. Description of the Background
Light-emitting materials that are used in organic light-emitting
devices are classified into fluorescent materials that use singlet
excitons and phosphorescent materials that use triplet excitons,
which differ in their emission mechanisms.
Generally, a phosphorescent material comprises an organic metal
compound that includes heavy atoms. In a phosphorescent material,
an exciton transitions from a triplet state to a singlet state and
emits light as a result. The phosphorescent material may use the
triplet excitons, which make up 75% of the excitons, and therefore
has much higher emission efficiency than the fluorescent material
that uses singlet excitons, which make up the remaining 25% of
excitons.
A light-emitting layer comprising a phosphorescent material
includes host material and a dopant material that receives energy
from the phosphorescent host material to emit light. Several
phosphorescent dopant materials using an iridium metal compound
have been reported by Princeton University and the University of
Southern California. Specifically, (4,6-F.sub.2ppy).sub.2Irpic and
an iridium compound based on a fluorinated ppy ligand structure
have been developed as blue light-emitting materials. Their host
material is typically 4,4'-biscarbazolylbiphenyl (CBP). It has been
reported that a triplet state energy band gap of a CBP molecule is
appropriate for producing green and red light, but since the energy
band gap of a CBP molecule is less than the energy gap of a blue
material, a very inefficient endothermic energy transition may be
required to produce blue light. As a result, a CBP host causes a
blue light-emitting material to have low emission efficiency and a
short lifespan.
Recently, a carbazole-based compound that has a larger triplet
energy band gap than CBP has been used when forming the
light-emitting layer with a phosphorescent material.
However, when a conventional carbazole-based compound is used, a
phosphorescence device may be inefficient and have a short
lifespan, and may have much room for improvement.
SUMMARY OF THE INVENTION
The present invention provides an organic light-emitting device
that may have improved emission efficiency and lifespan.
Additional features of the invention will be set forth in the
description which follows, and in part will be apparent from the
description, or may be learned by practice of the invention.
The present invention discloses an organic light-emitting device
comprising a first electrode, a second electrode, and a
light-emitting layer interposed between the first electrode and the
second electrode. The light-emitting layer comprises a
phosphorescent dopant and a phosphorescent host comprising at least
two hole transport materials.
The present invention also discloses an organic light-emitting
device comprising a first electrode, a second electrode, and a
light-emitting layer interposed between the first electrode and the
second electrode. The light-emitting layer comprises a
phosphorescent dopant, a first phosphorescent host having that has
a triplet energy of about 2.3 eV to about 3.5 eV and a second
phosphorescent host that has a triplet energy of about 2.3 eV to
about 3.5 eV. The first phosphorescent host and the second
phosphorescent host have different highest occupied molecular
orbital (HOMO) energy levels or different lowest unoccupied
molecular orbital (LUMO) energy levels.
It is to be understood that both the foregoing general description
and the following detailed description are exemplary and
explanatory and are intended to provide further explanation of the
invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are included to provide a further
understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention.
FIG. 1 is an energy diagram of a light-emitting layer of an organic
light-emitting device according to the present invention.
FIG. 2 illustrates an energy level of an organic light-emitting
device according to the present invention.
FIG. 3 is a sectional view of an organic light-emitting device
according to an exemplary embodiment of the present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
The organic light-emitting device of the present invention
comprises a light-emitting layer that comprises at least two hole
transport materials as phosphorescent hosts and a phosphorescent
dopant, to improve the emission efficiency and lifespan of the
organic light-emitting device.
According to an exemplary embodiment of the present invention, an
organic light-emitting device includes a first electrode, a second
electrode, and a light-emitting layer interposed between the first
electrode and the second electrode. The light-emitting layer
comprises a phosphorescent dopant and a phosphorescent host that
comprises at least two hole transport materials. At least two hole
transport materials are used to increase a recombination
probability in the light-emitting layer, thereby improving the
device's efficiency and lifespan.
The hole transport materials may include a first hole transport
material and a second hole transport material. The first hole
transport material and the second hole transport material may have
different highest occupied molecular orbital (HOMO) energy levels
or different lowest unoccupied molecular orbital (LUMO) energy
levels.
When the first hole transport material and the second hole
transport material do not have the same energy levels, the injected
holes and electrons move at a more stable energy level. Therefore,
the holes and the electrons have a high recombination probability
within the light-emitting layer, and charges are not transferred
out of the light-emitting layer. When the two materials have the
same energy levels, this effect cannot be obtained. Thus, when the
two materials have a different HOMO energy level or a different
LUMO energy level charges can move at a stable energy level.
The triplet energy of the phosphorescent host refers to an energy
difference between a ground singlet state and a triplet state. The
triplet energy of each of the first hole transport material and the
second hole transport material is preferably about 2.3 eV to about
3.5 eV. If the triplet energy is less than 2.3 eV, energy is
inefficiently transferred to the phosphorescent dopant, thereby
degrading the operating characteristics of the device. If the
triplet energy is greater than 3.5 eV, a driving voltage rises
undesirably or the efficiency decreases.
The first hole transport material and the second hole transport
material are preferably carbazole-based compounds.
Examples of the carbazole-based compounds may include, but are not
limited to 1,3,5-tricarbazolylbenzene, 4,4'-biscarbazolylbiphenyl
(CBP), polyvinylcarbazole, m-biscarbazolylphenyl,
4,4'-biscarbazolyl-2,2'-dimethylbiphenyl (dmCBP),
4,4'4''-tri(N-carbazolyl)triphenylamine,
1,3,5-tris(2-carbazolylphenyl)benzene,
1,3,5-tris(2-carbazolyl-5-methoxyphenyl)benzene and
bis(4-carbazolylphenyl)silane.
CBP is preferably used as the first hole transport material and the
second hole transport material preferably comprises materials that
have a broader band gap than CBP. Under these conditions, charges
effectively recombine in the light-emitting layer to increase the
emission efficiency.
The first hole transport material and the second hole transport
material may have a mixing weight ratio of about 1:3 to about 3:1,
and preferably about 3:1. If the concentration of the first hole
transport material is less than the above range, the operating
characteristics do not improve in comparison with using a single
host. If the concentration of the first hole transport material is
greater than the above range, the emission efficiency does not
improve.
The light-emitting layer may comprise about 70 parts by weight to
about 99 parts by weight of the phosphorescent hosts and about 1
part by weight to about 30 parts by weight of the phosphorescent
dopant based on 100 parts by weight of the light-emitting layer. If
the concentration of the phosphorescent hosts is less than 70 parts
by weight, triplet quenching occurs, thereby reducing the emission
efficiency. If the concentration of the phosphorescent hosts is
greater than 99 parts by weight, the light-emitting material is
ineffective, thereby reducing the emission efficiency and the
lifespan of the resulting device.
The phosphorescent dopant used in the formation of the
light-emitting layer may be represented by Ir(L)3 or Ir(L)2L', in
which L and L' are selected from the following structures:
##STR00001## ##STR00002##
The light-emitting material may include, but is not limited to,
bisthienylpyridine acetylacetonate iridium,
bis(benzothienylpyridine)acetylacetonate iridium,
bis(2-phenylbenzothiazole)acetylacetonate iridium,
bis(1-phenylisoquinoline)iridium acetylacetonate,
tris(1-phenylisoquinoline), tris(phenylpyridine)iridium,
tris(2-phenylpyridine)iridium, tris(2-phenylpyridine)iridium,
tris(3-biphenylpyridine)iridium, tris(4-biphenylpyridine)iridium,
and the like.
The light-emitting layer preferably comprises a phosphorescent
dopant and CBP and dmCBP as phosphorescent hosts. In particular,
the phosphorescent dopant is (2-phenylpyridine)iridium
[Ir(ppy).sub.3] and its concentration is preferably about 1 part by
weight to about 3 parts by weight based on 100 parts by weight of
the light-emitting layer. When the concentration of the
phosphorescent dopant is less than 1 part by weight, the emission
efficiency and lifespan of the resulting device are reduced. When
the concentration of the phosphorescent dopant is greater than 30
parts by weight, concentration quenching occurs, thereby reducing
the emission efficiency.
The organic light-emitting device according to an exemplary
embodiment of the present invention may further comprise at least
one of a hole injection layer and a hole transport layer interposed
between the first electrode and the light-emitting layer. The
organic light-emitting device according to an exemplary embodiment
of the present invention may further comprise at least one of a
hole blocking layer, an electron transport layer, and an electron
injection layer interposed between the light-emitting layer and the
second electrode.
According to another exemplary embodiment of the present invention,
a phosphorescent dopant is used to form a light-emitting layer. The
light-emitting layer further includes a first phosphorescent host
and a second phosphorescent host with a triplet energy of about 2.3
eV to about 3.5 eV. When the first phosphorescent host and the
second phosphorescent host have different HOMO energy levels and/or
different LUMO energy levels, the recombination efficiency of holes
and electrons is increased, thereby improving emission
efficiency.
If the triplet energy of the phosphorescent host is less than 2.3
eV, energy is inefficiently transferred to the phosphorescent
dopant. If the triplet energy is greater than 3.5 eV, the driving
voltage rises. Additionally, if the difference between the HOMO
energy level of the first phosphorescent host and the HOMO energy
level of the second phosphorescent host is zero, and the difference
between the LUMO energy level of the first phosphorescent dopant
and the LUMO energy level of the second phosphorescent dopant is
zero, the emission efficiency is reduced.
The first phosphorescent host may have a HOMO energy level of about
5.5 eV to about 7.0 eV, and a LUMO energy level of about 2.1 eV to
about 3.5 eV. The second phosphorescent host may have a HOMO energy
level of about 5.5 eV to about 7.0 eV, and a LUMO energy level of
about 2.1 eV to about 3.5 eV. The first phosphorescent host and the
second phosphorescent host are selected to satisfy the conditions
of the HOMO and LUMO energy levels.
Further, the first phosphorescent host is selected to have less
triplet energy than the second phosphorescent host. Additionally,
each of the first phosphorescent host and the second phosphorescent
host may have an energy band gap of about 2.5 eV to about 4.0 eV
between the HOMO and LUMO energy levels.
FIG. 1 is an energy level diagram of the light-emitting layer of
the organic light-emitting device according to an exemplary
embodiment of the present invention, and FIG. 2 illustrates the
energy level of the organic light-emitting device according to the
present invention.
An embodiment of the present invention will now be described with
reference to FIG. 1 and FIG. 2. The phosphorescent dopant may
comprise, tris(2-phenylpyridine)iridium (Ir(PPy).sub.3), for
example.
In order to allow an energy transition in the light-emitting layer
comprised of a phosphorescent material, the triplet energy of the
phosphorescent host is greater than the triplet energy of the
phosphorescent dopant. Accordingly, the triplet energy of the
phosphorescent host has a longer wavelength than a red
light-emitting material. Therefore, the phosphorescent host
preferably has a triplet energy of 2.3 eV or greater. Additionally,
since the first phosphorescent host and the second phosphorescent
host do not have the same energy levels in the present embodiment,
the injected holes and electrons move at a more stable energy
level. Therefore, the holes and the electrons have a high
recombination probability in the light-emitting layer, and charges
are not transferred out of the light-emitting layer.
On the other hand, if the first phosphorescent host and the second
phosphorescent host have the same energy level, the above-described
effect is not generated. Accordingly, the first phosphorescent host
and the second phosphorescent host should have different HOMO and
LUMO energy levels to move the electrons at the stable energy
level.
In FIG. 1, S.sub.1.sup.H denotes a singlet excited state of the
phosphorescent host, S.sub.0.sup.H denotes a singlet ground state
of the phosphorescent host, T.sub.1.sup.H denotes a triplet excited
state of the phosphorescent host, S.sub.1.sup.G denotes a singlet
excited state of the phosphorescent dopant, S.sub.0.sup.G denotes a
singlet ground state of the phosphorescent dopant, and T1 and T2
respectively denote triplet excited states of the phosphorescent
dopant.
The first phosphorescent host and the second phosphorescent host
may include, but are not limited to 4,4'-biscarbazolylbiphenyl
(CBP) (triplet energy: 2.56 eV, HOMO=5.8 eV, LUMO=3.0 eV),
2,9-dimethyl-4,7-diphenyl-9,10-phenanthroline (BCP) (triplet
energy: 2.5 eV, HOMO=6.3 eV, LUMO=3.0 eV), and BAlq3 (triplet
energy: 2.4 eV, HOMO=5.9 eV, LUMO=2.8 eV).
The first phosphorescent host and the second phosphorescent host
may have a mixing weight ratio of about 10:90 to about 90:10.
The light-emitting layer may comprise about 70 parts by weight to
about 99 parts by weight of the phosphorescent host and about 1
part by weight to about 30 parts by weight of the phosphorescent
dopant based on 100 parts by weight of the light-emitting layer. If
the concentration of the phosphorescent host is less than 70 parts
by weight, triplet quenching occurs, thereby reducing the emission
efficiency. If the concentration of the phosphorescent host is
greater than 99 parts by weight, the light-emitting material is
ineffective, thereby reducing the emission efficiency and the
lifespan of the resulting device.
The phosphorescent dopant is the light-emitting material. The
light-emitting material may include, but is not limited to
bisthienylpyridine acetylacetonate iridium,
bis(benzothienylpyridine)acetylacetonate iridium,
bis(2-phenylbenzothiazole)acetylacetonate iridium,
bis(1-phenylisoquinoline)iridium acetylacetonate,
tris(1-phenylisoquinoline)iridium, tris(2-phenylpyridine)iridium
(Ir(PPy).sub.3), tris(2-biphenylpyridine)iridium,
tris(3-biphenylpyridine)iridium, tris(4-biphenylpyridine)iridium,
and the like.
FIG. 3 is a sectional view of an organic light-emitting device
according to an exemplary embodiment of the present invention.
Referring to FIG. 3, a method for fabricating the organic
light-emitting device according to an exemplary embodiment of the
present invention will now be described.
First, an anode material is coated on a substrate to form an anode
as a first electrode. Here, the substrate is any general substrate
that may be used in a general organic light-emitting device. The
substrate may be a waterproof organic substrate that has excellent
transparency, surface smoothness, and easy treatment, or it may be
a transparent plastic substrate. The anode may be formed of indium
tin oxide (ITO), indium zinc oxide (IZO), tin dioxide (SnO.sub.2),
zinc oxide (ZnO) or the like.
A hole injection layer material is vacuum thermally-deposited or
spin-coated on the anode to selectively form a hole injection layer
(HIL). The hole injection layer may be about 50 .ANG. to about 1500
.ANG. thick. If the hole injection layer is less than 50 .ANG.
thick, hole injection characteristics may deteriorate. If the hole
injection layer is greater than 1500 .ANG. thick, the driving
voltage increases.
The hole injection layer may comprise copper phthalocyanine (CuPc),
or TCTA, m-MTDATA and IDS 406 (Idemitz, Inc.), which are
Starburst-type amines, but is not specifically limited to these
materials.
##STR00003##
A hole transport layer material is thermally-evaporated or
spin-coated on the hole injection layer to selectively form a hole
transport layer (HTL). The hole transport layer may include, but is
not limited to
N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1-biphenyl]-4,4'-diamine
(TPD), N,N'-di(naphthalene-1-yl)-N,N'-diphenyl benxidine (NPD),
IDE320 (Itemitz, Inc.),
N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine
(NPB), and the like. The hole transport layer may be about 50 .ANG.
to about 1500 .ANG. thick. If the hole transport layer is less than
50 .ANG. thick, hole transport characteristics deteriorate. If the
hole transport layer is greater than 1500 .ANG. thick, the driving
voltage increases.
##STR00004##
Next, a first phosphorescent host and a second phosphorescent host
that satisfy the above energy conditions are used together with a
phosphorescent dopant to form a light-emitting layer (EML) on the
hole transport layer. The light-emitting layer may be formed by
vacuum deposition, ink jet printing, laser induced thermal imaging,
photolithography or the like, but is not limited thereto.
The light-emitting layer may be about 100 .ANG. to about 800 .ANG.
thick, and in particular, about 300 .ANG. to about 400 .ANG.. If
the light-emitting layer is less than 10 .ANG. thick, the
efficiency and the lifespan of the light-emitting layer may
decrease. If the light-emitting layer is greater than 800 .ANG.
thick, the driving voltage may increase.
A hole blocking layer material may be vacuum-deposited or
spin-coated on the light-emitting layer to form a hole blocking
layer (HBL) (not shown), if necessary. The hole blocking layer
material is not particularly limited, but may have an electron
transporting ability and a higher ionization potential than the
light-emitting compound. Examples of such a material include Balq,
BCP, TPBI, etc. The HBL is about 30 .ANG. to about 500 .ANG. thick.
If the HBL is less than 30 .ANG. thick, the hole blocking property
is poor. If the HBL is greater than 500 .ANG. thick, the driving
voltage increases.
##STR00005##
An electron transport layer (ETL) may be formed on the HBL or the
EML by vacuum deposition or spin coating. The electron transport
layer may comprise, but is not limited to Alq3. The electron
transport layer may be about 50 .ANG. thick to about 600 .ANG.
thick. If the electron transport layer is less than about 50 .ANG.
thick, the lifespan of the electron transport layer decreases. If
the electron transport layer is greater than 600 .ANG. thick, the
driving voltage increases.
Further, an electron injection layer (EIL) may be selectively
formed on the electron transport layer. The electron injection
layer may comprise LiF, NaCl, CsF, Li.sub.2O, BaO, Liq or the like.
The electron injection layer may be about 1 .ANG. thick to about
100 .ANG. thick. If the electron injection layer is less than 1
.ANG. thick, it functions ineffectively, thereby increasing the
driving voltage. If the electron injection layer is greater than
100 .ANG. thick, it functions as an insulating layer, thereby
increasing the driving voltage.
##STR00006##
Next, a cathode metal is vacuum thermally-deposited on the electron
injection layer (EIL) to form a cathode as a second electrode,
thereby completing the organic light-emitting device.
The cathode metal may include, but is not limited to lithium,
magnesium, aluminium, aluminium-lithium, calcium, magnesium-indium,
magnesium-silver, and the like.
The organic light-emitting device according to an exemplary
embodiment of the present invention may further comprise one or two
intermediate layers depending on the compositions of the anode, the
hole injection layer, the hole transport layer, the light-emitting
layer, the electron transport layer, the electron injection layer,
and the cathode. In addition to the aforementioned layers, an
electron blocking layer may be embedded in the organic
light-emitting device.
Hereinafter, the present invention will be described using the
following example, which is not intended to limit the present
invention.
Example 1
In order to prepare an anode, a 15 .OMEGA./cm.sup.2 (1200 .ANG.)
ITO glass substrate (Corning Inc.) was cut to a size of 50
mm.times.50 mm.times.0.7 mm, and then the cut glass substrate was
rinsed using ultrasonic waves for five minutes in each of isopropyl
alcohol and deionized water, and then the rinsed glass substrate
was exposed to ultraviolet rays and ozone for thirty minutes.
Then, N,N'-di(1-naphthyl)-N,N'-diphenyl-benzidine (NPD) was
vacuum-deposited on the substrate to form a 600 .ANG. thick hole
transport layer.
90 parts by weight of CBP and 10 parts by weight of dmCBP based on
100 parts by weight of host materials and 5 parts by weight of
Ir(PPy).sub.3 as a phosphorescent dopant based on 100 parts by
weight of the light-emitting layer were vacuum-deposited on the
hole transport layer to form a 400 .ANG. light-emitting layer.
Alq3 was deposited on the light-emitting layer to form a 300 .ANG.
thick electron transport layer.
A 10 .ANG. thick electron injection layer comprising LiF and a 1000
.ANG. thick cathode comprising Al were sequentially
vacuum-deposited on the electron transport layer to form a LiF/Al
electrode, thereby forming the organic light-emitting device.
Example 2
An organic light-emitting device was fabricated in the same manner
as in Example 1, except that 75 parts by weight of CBP and 25 parts
by weight of dmCBP were used to form the light-emitting layer.
Example 3
An organic light-emitting device was fabricated in the same manner
as in Example 1, except that 50 parts by weight of CBP and 50 parts
by weight of dmCBP were used to form the light-emitting layer.
Example 4
An organic light-emitting device was fabricated in the same manner
as in Example 1, except that 25 parts by weight of CBP and 75 parts
by weight of dmCBP were used to form the light-emitting layer.
Example 5
An organic light-emitting device was fabricated in the same manner
as in Example 1, except that 10 parts by weight of CBP and 90 parts
by weight of dmCBP were used to form the light-emitting layer.
Comparative Example 1
In order to prepare an anode, a 15 .OMEGA./cm.sup.2 (1200 .ANG.)
ITO glass substrate (Corning Inc.) was cut to a size of 50
mm.times.50 mm.times.0.7 mm, and then the cut glass substrate was
rinsed using ultrasonic waves for five minutes in each of isopropyl
alcohol and deionized water using ultrasonic waves, and then the
rinsed glass substrate was exposed to ultraviolet rays and ozone
for thirty minutes.
Then, NPD was vacuum-deposited on the substrate to form a 600 .ANG.
hole transport layer. 100 parts by weight of CBP based on 100 parts
by weight of the host material and 10 parts by weight of
Ir(PPy).sub.3 as a phosphorescent dopant were vacuum-deposited on
the hole transport layer to form a 400 .ANG. light-emitting
layer.
Alq3 as an electron transport material was deposited on the
light-emitting layer to form a 300 .ANG. thick electron transport
layer.
A 10 .ANG. thick electron injection layer comprising LiF and a 1000
.ANG. cathode comprising Al were sequentially vacuum-deposited on
the electron transport layer to form a LiF/Al electrode, thereby
forming the organic light-emitting device as illustrated in FIG.
1.
Comparative Example 2
An organic light-emitting device was manufactured in the same
manner as in Comparative Example 1, except that 100 parts by weight
of dmCBP based on 100 parts by weight of the host material and 10
parts by weight of Ir(PPy).sub.3 as a phosphorescent dopant were
used to form a light-emitting layer.
The organic light-emitting devices that were fabricated in Example
1, Example 2, Example 3, Example 4, Example 5, Comparative Example
1, and Comparative Example 2 were tested for emission efficiency
and lifetime characteristics.
The emission efficiency was measured using a spectrometer and the
lifespans were evaluated using a photodiode. The results are
indicated in Table 1.
The organic light-emitting devices of Comparative Example 1 and
Comparative Example 2 had an emission efficiency of about 24 cd/A
and 22 cd/A, respectively, and the organic light-emitting devices
of Examples 2 and 3 had the emission efficiency of 30 cd/A. Thus,
the organic light-emitting devices of the present invention have
improved emission efficiency.
The lifespan is determined as the time it takes for an initial
emission brightness to be reduced by 50%. The lifespan of the
organic light-emitting device of Example 2 was 8,000 hours at 1000
cd/m.sup.2 and lifetimes of the organic light-emitting devices of
Comparative Example 1 and Comparative Example 2 were 5,000 hours
and 4,000 hours, respectively, at 1000 cd/m.sup.2. Thus, it can be
seen that the organic light-emitting devices of the present
invention have improved lifespans.
TABLE-US-00001 TABLE 1 CBP:dmCBP Efficiency (cd/A) Lifetime (h)
Example 1 90:10 25 5500 Example 2 75:25 30 8000 Example 3 50:50 30
7000 Example 4 25:75 28 7000 Example 5 10:90 23 5000 Comparative
100:0 24 5000 Example 1 Comparative 0:100 22 4000 Example 2
Example 6
In order to obtain an anode, a 15 .OMEGA./cm.sup.2 (1200 .ANG.) ITO
glass substrate (Corning Inc.) was cut to a size of 50 mm.times.50
mm.times.0.7 mm, and then the cut glass substrate was rinsed in
each of isopropyl alcohol and deionized water using ultrasonic
waves for five minutes, and then the rinsed glass substrate was
exposed to ultraviolet rays and ozone for thirty minutes.
Then, N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benxidine (NPD) was
vacuum-deposited on the substrate to form a 600 .ANG. hole
transport layer.
75 parts by weight of CBP and 25 parts by weight of BCP based on
100 parts by weight of the host materials and 5 parts by weight of
Ir(PPy).sub.3 based on 100 parts by weight of the light-emitting
layer were vacuum-deposited on the hole transport layer to form a
400 .ANG. thick light-emitting layer.
Alq3 was deposited on the light-emitting layer to form a 300 .ANG.
thick electron transport layer.
A 10 .ANG. thick electron injection layer comprising LiF and a 1000
.ANG. thick cathode comprising Al were sequentially
vacuum-deposited on the electron transport layer to form a LiF/Al
electrode, thereby forming the organic light-emitting device.
Comparative Example 3
An organic light-emitting device was fabricated in the same manner
as in Example 6, except that Alq3 (triplet energy: 2.0 eV, HOMO=5.8
eV, LUMO=3.0 eV) was used instead of BCP to form the light-emitting
layer.
Comparative Example 4
An organic light-emitting device was fabricated in the same manner
as Example 6, except that BCP was not used to form the
light-emitting layer.
The organic light-emitting devices fabricated in Example 6,
Comparative Example 3, and Comparative Example 4 were tested for
emission efficiency and lifespan.
The organic light-emitting device of Comparative Example 3 had an
emission efficiency of about 10 cd/A and a lifespan of 1000 h
(@1000 cd/m.sup.2). The organic light-emitting device of
Comparative Example 4 had an emission efficiency of about 24 cd/A
and a lifespan of 5000 h (@1000 cd/m.sup.2). The organic
light-emitting device of Example 6 had an emission efficiency of
about 32 cd/A and a lifespan of 10,000 h (@1000 cd/m.sup.2). In
comparison with Comparative Example 4, the organic light-emitting
device of Example 6 had better emission efficiency and lifespan.
The obtained results are indicated in Table 2.
TABLE-US-00002 TABLE 2 Host material Efficiency (cd/A) Lifetime (h)
Example 6 CBP, BCP 32 10000 Comparative CBP, Alq3 10 1000 Example 3
Comparative CBP 24 5000 Example 4
It will be apparent to those skilled in the art that various
modifications and variation can be made in the present invention
without departing from the spirit or scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *